Position measuring apparatus and method

ABSTRACT

A position measuring apparatus receives at least one precise position information set from at least one visible-light wireless communication device including a transmission light source, and upon receipt of the at least one precise position information ser, acquires a virtual distance based on the positions of transmission light sources imaged on an image sensor. Next, the position is measured according to the precise position information and the actual distance, virtual distance, and image sensor inclination based on this information.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2010-0130172 and 10-2011-0048676 filed in the KoreanIntellectual Property Office on Dec. 17, 2010 and May 23, 2011, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a position measuring apparatus andmethod, and more particularly, to a position measuring apparatus andmethod using an image sensor.

(b) Description of the Related Art

In general, a global positioning system (GPS) is used to measure theposition of an object. In a GPS method, the distance from a GPSsatellite to a measurement object is calculated by receiving positioninginformation from the GPS satellite and measuring the time taken toreceive the positioning information. The distance from one GPS satelliteis equal at any location on the globe as far away as the GPS satellite.If three or more of such information, that is, trajectory information(longitude and latitude) and distance of three satellites are obtained,a point where virtual spheres formed by the three GPS satellites meet iscreated, and this point serves as the position of a measurement object.However, an error may occur in such GPS-based position informationdepending on the accuracy of positioning information provided by the GPSsatellites and the accuracy of current time information required forcalculating the distance from the GPS satellites. The error can beseveral tens of meters. Another disadvantage is that no GPS satellitesignal can be received indoors.

To overcome these disadvantages, the position information of a basestation to which a mobile terminal is connected or the positioninformation of a connection in a wireless LAN such as WiFi may be used.However, one of the major drawbacks of such a position informationservice using radio waves is that it is difficult to providethree-dimensional position information. In other words, informationabout the presence of a measurement object in a certain building can beacquired; however, information about on which floor or in which room theobject is located is hardly obtained. In order to overcome thesedisadvantages, a position measurement technique based on positioninformation by using the visible light wireless communication technologyhas been proposed. In this case, position information about ameasurement object may even include details like the floor, room, etc.of a building where the measurement object is placed.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a positionmeasuring apparatus and method that allow more accurate positionmeasurement using the visible light wireless communication technology.

An exemplary embodiment of the present invention provides a positionmeasuring method, which measures a position based on informationprovided from at least one communication device including a transmissionlight source, the method including: acquiring precise positioninformation indicating a position of the transmission light source bycapturing an image including an optical signal transmitted from thetransmission light source; calculating an actual light source distancebetween transmission light sources based on the precise positioninformation; calculating a virtual light source distance between thetransmission light sources imaged on the image sensor from the capturedimage; measuring an inclination of the image sensor; and measuring theposition based on the actual light source distance, the virtual lightsource distance, and the inclination.

The position measuring includes: calculating a first virtual lightsource distance between the transmission light sources imaged on theimage sensor, and a second virtual light source distance correspondingto a parallel state of the image sensor based on the inclination; andcalculating the position based on the second virtual light sourcedistance, the actual light source distance, and the received preciseposition information regarding each transmission light source.

Another embodiment of the present invention provides a positionmeasuring method, which measures a position based on informationprovided from at least one communication device including a transmissionlight source, the method including: acquiring precise positioninformation indicating a position of the transmission light source bycapturing an image including an optical signal transmitted from thetransmission light source with an image sensor, the precise positioninformation including coordinates along X and Y axes on atwo-dimensional plane using the X and Y axes; if the precise positioninformation is received from at least two transmission light sources,calculating an actual light source distance between the transmissionlight sources on each of the X and Y axes based on the precise positioninformation; calculating a virtual light source distance between thetransmission light sources on each of the X and Y axes, imaged on theimage sensor, from the captured image; measuring an inclination of theimage sensor along each of the X and Y axes; calculating a parallelvirtual light source distance on each of the X and Y axes, correspondinga parallel state of the image sensor, based on the virtual light sourcedistance and the inclination; and measuring a position of a measurementobject on each of the X and Y axes based on the measured actual lightsource distance, parallel virtual light source distance, and inclinationand the precise position information.

Yet another embodiment of the present invention provides a positionmeasuring apparatus, which measures a position based on informationprovided from at least one communication device including a transmissionlight source, the apparatus including: a position information receiverthat acquires precise position information indicating a position of thetransmission light source by capturing an image including an opticalsignal transmitted from the transmission light source with a imagesensor, the precise position information including coordinates along Xand Y axes on a two-dimensional plane using the X and Y axes; an actuallight source distance measuring unit that calculates an actual lightsource distance between transmission light sources on each of the X andY axes based on the precise position information; a virtual light sourcedistance measuring unit that calculates a virtual light source distancebetween the transmission light sources on each of the X and Y axes,imaged on the image sensor, from the captured image; an inclinationmeasuring unit which measures an inclination of the image sensor alongeach of the X and Y axes; and a position information processing unitwhich measures a position of a measurement object on the X and Y axesbased on an actual light source distance, virtual light source distance,and inclination measured for each of the X and Y axes and the preciseposition information.

The position information processing unit includes: a distance measuringmodule that calculates a parallel virtual light source distance for eachof the X and Y axes, corresponding to the image sensor in a parallelstate based on the virtual light source distance and the inclination,and calculates the first and second distances for each of the X and Yaxes based on the parallel virtual light source distance, the firstdistance corresponding to a distance to a measurement position from theposition of one transmission light source based on the precise positioninformation, and the second distance corresponding to a distance to themeasurement position from the position of another transmission lightsource based on the precise position information; and a positioncalculation module that measures the position of the object on the X andY axes based on the first distance, the second distance, and the preciseposition information regarding the transmission light sources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the concept of position information provisionusing visible-light wireless communication according to an exemplaryembodiment of the present invention.

FIG. 2 is a view showing the positional relationship between the imagesensor and the transmission light sources according to the exemplaryembodiment of the present invention.

FIG. 3 is an illustrative diagram showing the positions of thetransmission light sources imaged on the image sensor according to theexemplary embodiment of the present invention.

FIG. 4 is an illustrative diagram showing the image sensor beinginclined at a predetermined angle to the transmission light sourcesaccording to the exemplary embodiment of the present invention.

FIG. 5 is a flowchart of a position measuring method according to theexemplary embodiment of the present invention.

FIG. 6 is a schematic view showing the structure of the positionmeasuring apparatus according to the exemplary embodiment of the presentinvention.

FIG. 7 is a detailed view showing the structure of the positionmeasuring apparatus according to the exemplary embodiment of the presentinvention.

FIG. 8 is a position measuring method according to another exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, only certain exemplaryembodiments of the present invention have been shown and described,simply by way of illustration. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention. Accordingly, the drawings and description are to be regardedas illustrative in nature and not restrictive. Like reference numeralsdesignate like elements throughout the specification.

Throughout the specification, unless explicitly described to thecontrary, the word “comprise” and variations such as “comprises” or“comprising” will be understood to imply the inclusion of statedelements but not the exclusion of any other elements.

Hereinafter, a position measuring apparatus and method according to anexemplary embodiment of the present invention will be described withreference to the accompanying drawings.

The position measuring apparatus and method according to the exemplaryembodiment of the present invention, position measurement is carried outbased on information provided from a wireless communication system usingvisible light.

Visible rays are rays having a wavelength in a range that is visible toa human eye. The wavelength of the visible rays corresponds to awavelength of 380 to 780 nm. A change in nature according to thewavelength is represented by each color within the visible rays. Thewavelength is shorter going from red to violet. Light having awavelength longer than red is referred to as infrared rays and lighthaving a wavelength shorter than violet is referred to as ultravioletrays. In monochromatic light, red is shown at a wavelength of 700 to 610nm, orange is shown at a wavelength of 610 to 590 nm, yellow is shown ata wavelength of 590 to 570 nm, green is shown at a wavelength of 570 to500 nm, blue is shown at a wavelength of 500 to 450 nm, and violet isshown at a wavelength of 450 to 400 nm. Various colors can berepresented by a mixture of colors having each wavelength.

Unlike ultraviolet rays or infrared rays, the visible rays are visibleto a person. Lighting that radiates in the visible ray region shouldmeet various requirements such as accurate color representation, or thelike. A Small amount of flickering is one of the requirements. Since ahuman being cannot recognize flickering of 200 times or more per second,lighting using a light emitting diode (LED) having fast flickeringperformance controls flickering using pulse width modulation (PWM) inorder to expand the lifespan of the LED while saving energy.

A communication technology using light in a communication area includesinfrared-ray data wireless communication (IrDA) using an infrared-rayarea, a visible-light wireless communication using visible light,optical communication using an optical fiber, etc. The infrared datacommunication is a technology for performing a communication by using aninfrared-ray area having a wavelength of 850 to 900 nm. Visible-lightwireless communication is a communication technology using a wavelengthin the range of 380 to 780 nm.

Such wireless communication using visible light (hereinafter, referredto as “visible-light wireless communication”) is a wirelesscommunication technology using a visible light area having a wavelengthof 380 to 780 nm, which is different from the wavelength used forinfrared communication. Also, a position information service isprovided. To this end, precise position information can be providedusing LED lighting.

FIG. 1 is a view showing the concept of position information provisionusing visible-light wireless communication according to an exemplaryembodiment of the present invention.

As shown in the attached FIG. 1, visible-light wireless communicationdevices 11, 12, . . . , 1 n (n is a positive integer, and referred to byreference numeral 1 for convenience of description) can provide positioninformation to a mobile terminal 2 including an image sensor (forexample, a camera). In this case, the visible-light wirelesscommunication device 1 includes a transmission light source L1, L2, . .. , Ln (n is a positive integer, and is referred by reference numeral Lfor convenience of description), and provides precise positioninformation to the mobile terminal 2 by means of the transmission lightsource L. The precise position information is position information ofthe visible-light wireless communication device 1, and may includevarious kinds of position information, such as floor, a room number, andmeasurements in meters/centimeters/millimeters, as well as the latitudeand longitude relative to the installation position of the visible-lightwireless communication device 1. The precise position informationprovided from the transmission light source L of the visible lightwireless communication device 1 can have a precision with which thedistance between the transmission light sources can be measured incentimeters, more precisely, in millimeters.

An LED can be used as the transmission light source L. The LED includesa white (W) LED, a red (R) LED, a green (G) LED, a blue (B) LED, and soon.

The mobile terminal 2 receives the precise position information providedfrom the visible-light wireless communication device 1. To this end, themobile terminal 2 receives the precise position information providedfrom the visible-light wireless communication device 1 by using an imagesensor, and a position measuring apparatus 100 according to theexemplary embodiment of the present invention measures the position ofthe mobile terminal using the precise position information received bythe mobile terminal and the inclination information of the mobileterminal obtained by itself. Although the position to be measured by theposition measuring apparatus 100 is substantially the position of themobile terminal in which the position measuring apparatus 100 isincluded, this position is measured based on the image sensor of theposition measuring apparatus 100 and therefore the position to bemeasured can be represented by the position of the image sensor or theposition of the mobile terminal.

The position measuring apparatus 100 receives signals transmitted from aplurality of transmission light sources by using the image sensor.

The image sensor captures the position information transmitted in theform of optical signals from the visible-light wireless communicationdevices 1 and outputs corresponding electrical signals. The image sensormay include a camera or the like. The acquisition of data, transmittedby the visible-light wireless communication device 1, from theelectrical signals captured by the image sensor is a well-known art, soa detailed description thereof will be omitted.

For example, in the environment where the position measuring apparatus100 is in communication with the plurality of visible-light wirelesscommunication devices 1, as shown in FIG. 1, the positional relationshipbetween two transmission light sources and the image sensor of theposition measuring apparatus 100 will now be discussed.

FIG. 2 is a view showing the positional relationship between the imagesensor and the transmission light sources according to the exemplaryembodiment of the present invention.

As shown in FIG. 2, an image sensor 111 of the position measuringapparatus 100 can receive precise position information from the twotransmission light sources L1 and L2. In this case, for example, withrespect to the axis on which the first transmission light source L1 andthe second transmission light source L2 are located, the image sensor111 is located at a position P1 which is spaced a first distance d1 awayfrom the first transmission light source L1 and spaced a second distanced2 away from the second transmission light source L2. In this case,given that the actual distances, the first distance d1 and seconddistance d2, are known, the position of the image sensor can be measuredbased on the precise position information transmitted from the firsttransmission light source L1 and the precise position informationtransmitted from the second transmission light source L2. That is, giventhat the position of the first transmission light source L1 is PI1 andthe position of the second transmission light source L2 is PI2, theactual position P1 of the image sensor 111 can be detected based onPI1+d1 or PI2−d2. The first distance d1 represents the actual distancefrom the actual position of one transmission light source to the actualposition of the image sensor, and the second distance d2 represents theactual distance from the actual position of another transmission lightsource to the actual position of the image sensor. Herein, the distancebetween the position PI1 of the first transmission light source L1 andthe position PI2 of the second transmission light source L2 is referredto as the actual light source distance.

In the exemplary embodiment of the present invention, in order to detectthe first distance d1 and second distance d2 to the image sensor 111with respect to the actual positions of the transmission light sourcesL1 and L2, the positions of the transmission light sources whoseinverted images are formed on the image sensor 111 are used.

For example, as shown in FIG. 2, it is assumed that the transmissionlight sources L1 and L2 are located on the same axis (e.g., on a ceilingof a building), and the image sensor 111 of the position measuringapparatus 100 is located on an axis parallel to the axis on which thetransmission light sources L1 and L2 are located. In this case, theimage sensor 111 captures images of the transmission light sources L1and L2 along with optical signals from the transmission light sources L1and L2, and therefore inverted images of the transmission light sourcesL1 and L2 are formed on the image sensor 111. In other words, as shownin FIG. 2, the image of the first transmission light source L1 is formedat the position SPI1 on the image sensor 111, and the image of thesecond transmission light source L2 is formed at the position SPI2 onthe image sensor 111. When the central point SC of the image sensor 111corresponds to the actual position P1 of the image sensor 111, the firstvirtual distance sd1 and the second virtual distance sd2 can be acquiredbased on the positions SPI1 and SPI2 of the transmission light sourcesimaged on the image sensor 111. The first virtual distance sd1 is thedistance between the position SPI1 of the first transmission lightsource, imaged on the image sensor 111, and the central point SC of theimage sensor, and corresponds to the first distance d1. The secondvirtual distance sd2 is the distance between the position SPI2 of thesecond transmission light source, imaged on the image sensor 111, andthe central point SC of the image sensor, and corresponds to the seconddistance d2. As described above, since the distance calculated based onthe positions of the transmission light sources imaged on the imagesensor is not the actual distance but the distance on the image sensor,it can be deemed as a virtual distance. For better comprehension andease of description, the distance between the transmission light sourcesimaged on the image sensor is referred to as a “virtual light sourcedistance”. The virtual light source distance between the firsttransmission light source L1 and the second transmission light source L2is indicated by “SD”.

The first distance d1 and the first virtual distance sd1 areproportional to each other, and the second distance d2 and the secondvirtual distance sd2 are proportional to each other. Accordingly, thefollowing conditions are met.d1:d2=sd1:sd2d1:d1+d2=sd1:sd1+sd2  [Equation 1]

Herein d1+d2 can be calculated based on the precise position informationabout the actual positions PI1 and PI2 of the transmission lightsources, and sd1 and sd2 can be calculated based on the positions SPI1and SPI2 of the transmission light sources imaged on the image sensor111. Accordingly, the value of d1 can be calculated from Equation 1 asfollows.d1=(d1+d2)×sd1/(sd1+sd2)  [Equation 2]

As d1, the first distance, can be calculated from the above Equation 2,d2, the second distance, can be calculated based on the calculated d1.

As the first distance d1 and the second distance d2 are acquired, theactual position P1 of the image sensor 111 can be detected from PI1+d1or PI2−d2. The actual position P1 of the image sensor 111, as measuredherein, represents the position on one axis. For example, it representsthe position on the X axis. The actual position P1 of the image sensor111 on the Y axis can also be measured through the above process.

Meanwhile, a distance on the image sensor can be converted into anactual distance. That is, it is possible to find out how far the pixeldistance from the pixels of the images of the transmission light sourcesformed on the image sensor actually is. The distance (virtual distance)on the image sensor can be measured based on the pixel distance. Thepixel distance includes a pixel size and a pixel interval.

As shown in FIG. 2, the virtual light source distance SD between thepositions SPI1 and SPI2 of the transmission light sources imaged on theimage sensor is proportional to the actual light source distance Ddepending on the precise position information PI1 and PI2 of thetransmission light sources. Thus the virtual distance (unit virtualdistance) between pixels can be calculated as follows.Unit virtual distance=(d1+d2)/(sd1+sd2)  [Equation 3]

Based on the unit virtual distance, the virtual distance on the imagesensor can be converted into an actual distance.

Meanwhile, the transmission light sources imaged on the image sensor maynot be located on a straight line, as shown in FIG. 2, with respect tothe central point SC of the image sensor.

FIG. 3 is an illustrative diagram showing the positions of thetransmission light sources imaged on the image sensor according to theexemplary embodiment of the present invention.

For example, as shown in FIG. 3, the transmission light sources imagedon the image sensor 111 may be located on different axes from each otherrelative to the central point SC of the image sensor 111. When thepositions imaged on the image sensor are represented on atwo-dimensional plane using the X axis and the Y axis as shown in FIG.3, it is assumed that the coordinates of the central point SC of theimage sensor 111 are (X, Y). In this case, the coordinates (X, Y) of thecentral point SC can correspond to the target position to be measured.

Let us suppose that the coordinates of the first transmission lightsource L1 is (A1, B1) and the coordinates of the second transmissionlight source L2 is (A2, B2), and the relationship of A1>A2 and B1>B2 isestablished. Also, let us suppose that the distance from the coordinates(A1, B1) of the first transmission light source L1 to the Y axis and thedistance therefrom to the X axis are x1 and y1, respectively, and thecoordinates (A2, B2) of the second transmission light source L2 to the Yaxis and the distance therefrom to the X axis are x2 and y2,respectively.

In this state, the coordinates of the central point SC of the imagesensor—i.e., current position (X, Y)—can be calculated as follows.X=A1−x1=A2+x2Y=B1−y1=B2+y2  [Equation 4]

Herein x1, x2, y1, and y2 can be measured based on pixel distance, andthen converted into actual distance based on unit virtual distance. Thatis, each of the virtual distances x1, x2, y1, and y2 are converted intoactual distances based on the unit virtual distances, and the actualposition corresponding to the coordinates (X, Y) of the central point ofthe image sensor can be measured based on the actual positions PI1 andPI2 of the transmission light sources respectively corresponding to thecoordinates (A1, B1) of the first transmission light source L1 and thecoordinates (A2, B2) of the second transmission light source L2 and theactual distances corresponding to the virtual distances x1, x2, y1, andy2.

The above-described method for measuring position on a two-dimensionalplane with the X axis and the Y axis also applies to a three-dimensionalplane. In this case as well, the axes along which the transmission lightsources lie and the image sensor should be parallel to each other.

Meanwhile, a measurement object, for example, a mobile terminal, whichis equipped with the image sensor, cannot always be kept parallel to theaxis along which the transmission light sources are mounted. In otherwords, a measurement object may be inclined at a predetermined angle tothe axis along which the transmission light sources are mounted.

FIG. 4 is an illustrative diagram showing the image sensor beinginclined at a predetermined angle to the transmission light sourcesaccording to the exemplary embodiment of the present invention.

As illustrated in FIG. 4, the image sensor may be inclined at apredetermined angle while being parallel to the axis along which thetransmission light sources are formed. Although FIG. 4 depicts theinclination toward only one axis, such inclination may occur along eachof the X axis and the Y axis.

For example, if the image sensor is located inclined (TS) at apredetermined angle from the parallel state (PS), it is assumed that theimage sensor is in the parallel state (PS) based on the distance betweenthe transmission light sources obtained from the image captured by theimage sensor in the inclined state (TS). Thus, the distance between thetransmission light sources on the image captured by the image sensor inthe parallel state can be taken into account. For better comprehensionand ease of description, if the distance between the transmission lightsources obtained from the image actually captured by the image sensorcurrently in the inclined state is referred to as a “first virtualtransmission light source distance”, the distance between thetransmission light sources captured by the image sensor assumed to be inthe parallel state may be referred to as a “second virtual light sourcedistance”.

The first and second virtual light source distances between thetransmission light sources are in the relationship shown in FIG. 4.

The first virtual light source distance is measured upon receivingoptical signals from the transmission light sources when the imagesensor 111 of the position measuring apparatus 100 is in the inclinedstate (TS); however, an error occurs if the first virtual light sourcedistance is used as it is. An error in units of pixel distance appearsto be more serious when converted into actual distance. Therefore, inthe exemplary embodiment of the present invention, such an error iscompensated based on information on the inclination of the image sensor.

To this end, the second virtual light source b+c, which is the distancebetween the transmission light sources imaged on the image sensor in theparallel state (PS) is required. This is to acquire the virtual distancecorresponding to the actual distance between the transmission lightsources as shown in FIG. 2.

In order to calculate the second virtual light source distance b+c whenthe first virtual image light source distance a is acquired from theimage captured by the image sensor in the inclined state (TS), theinclination α for the inclined state (TS) is measured, and the secondvirtual light source distance is calculated based on the measuredinclination α. Meanwhile, if the central point SC of the image sensor ischanged from the inclined state to the parallel state based on theinclination, it is placed at a predetermined position SC′ as shown inFIG. 4. The distance between the central point SC′ of the image sensorin the parallel state and a given transmission light source imaged onthe image sensor in the parallel state can be referred to as “g”. The“g” corresponds to the first virtual distance sd1 of FIG. 2. Forconvenience of description, g represents the first 1-1 virtual distance.

In FIG. 4, if a straight line perpendicular from the position of acertain transmission light source imaged on the image sensor in theinclined state (TS) to the image sensor in the parallel state (TS) isdefined as virtual distance h, a right triangle having a virtual heighth whose hypotenuse is the first virtual light source distance a isformed. The base of the right triangle is referred to as a virtual baseb, and the following relationship is established using the righttriangle.b=a×cos αh=a×sin αγ=90−α  [Equation 5]

Herein α represents the angle of inclination of the image sensor 111,and corresponds to the angle between the hypotenuse a and the base b ofthe right triangle.

In the right triangle shown in FIG. 4, in order to know the anglebetween β and δ under the condition that the sum of β, γ, and δ is 180°,a right triangle whose height is the focal distance f of the imagesensor in the inclined state (TS) and whose base angle is γ is formed,and the base of the right triangle is denoted by “e”. Then, thefollowing condition is met for β and δ.tan β=f/e→β=tan⁻¹ (f/e)δ=180−β−γ=180−β−(90−α)=90−β+α  [Equation 6]

Through the above procedure, the angles β and δ are calculated. Thus,the angle of γ can be estimated based on the angles β and δ.

As the angle δ has been calculated, the value of c constituting thesecond virtual light source distance can be calculated as follows.

$\begin{matrix}{c = {{h \times \tan\;\delta} = {{\left( {a \times \sin\;\alpha} \right) \times \tan\;\delta} = {\left( {a \times \sin\;\alpha} \right) \times {\tan\left( {90 - \beta + \alpha} \right)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Moreover, the 1-1 virtual distance g, which is the distance from thecentral point SC′ of the image sensor in the parallel state to thetransmission light source, is calculated. Specifically, the hypotenuse ican be obtained from a right triangle whose height is the focal distancef of the image sensor in the inclined state (TS), whose base angle is β,and whose base is “e”, and the hypotenuse d can be obtained from a righttriangle whose height is the virtual height h, whose base is “c”, andwhich has one angle δ. Therefore, the base g, i.e., the 1-1 virtualdistance, can be calculated from a right angle whose hypotenuse is i+d,whose height is k, whose base is g, and which has one angle δ.

Moreover, based on the first virtual light source distance a, which isthe distance between the transmission light sources imaged on the imagesensor in the inclined state (TS), and the inclination α of the imagesensor, the second virtual light source distance between thetransmission light sources on the image sensor assumed to be in theparallel state (PS) can be represented as follows.Second virtual light source distance (b+c)=a×cos α+{(a×sin α)×tan (90−β+α)}  [Equation 8]

As above, once the second virtual light source distance is acquired, theactual light source distance can be estimated based on the relationshipbetween the distance (second virtual light source distance) between thetransmission light sources on the image sensor and the actual distancebetween the transmission light sources as illustrated in FIG. 2.Specifically, the second virtual light source distance b+c and the 1-1virtual distance g correspond to the virtual light source distance SDand the first virtual distance sd1, respectively, as shown in FIG. 2.Therefore, the second virtual distance sd2 can be calculated from thevirtual light source distance SD and the first virtual distance sd1.Moreover, as the first distance d can be calculated by the aboveEquation 2 by using d1+d2, the first virtual distance sd1, and thesecond virtual distance sd2 acquired based on received precise positioninformation, the second distance d2 can be calculated based on thecalculated first distance d1. As the first distance d1 and the seconddistance d2 are acquired, the actual position P1 of the image sensor 111in the environment as in FIG. 2 can be estimated from PI1+d1 or PI2−d2.

In the above description, every distance and inclination is representedalong only one axis; however, in order to measure position on atwo-dimensional plane including two axes, virtual distance, actual lightsource distance, and virtual light source distance, inclination, etc.along each axis (X axis and Y axis) have to be taken into consideration.

FIG. 5 is a view showing the flow of a position measuring methodaccording to the exemplary embodiment of the present invention based onthe above-described procedure.

As shown in FIG. 5, in order to measure the position of the imagesensor, first of all, the position measuring apparatus 100 acquires thefocal distance f of the image sensor 111 (S100). Next, virtualcoordinates, which are the positions of the transmission light sourcesimaged on the image sensor 111, are acquired (S110).

The first virtual light source distance a on the image sensor in theinclined state is acquired based on the acquired virtual coordinates(S120), the inclination α of the image sensor is measured (S130), andthe virtual height (h) is acquired (S140). Supposing that the imagesensor is in the parallel state based on the virtual height h, themeasured inclination α, and the first virtual light source distance a,the second virtual light source distance b+c is calculated (S150). Thefirst virtual distance (sd1, g) and the second virtual distance sd2,which are the distances from the central point of the image sensor tothe imaged transmission light sources are acquired based on the secondvirtual transmission light source b+c (S160).

Next, the first distance d1 and the second distance d2, which are theactual distances depending on the actual positions of the light sources,are calculated based on the second virtual light source distance b+c,the first virtual distance sd1, and the second virtual distance sd2(S170). Then, the position of the image sensor is acquired based on thecalculated first and second distances d1 and d2 and the actual positionsof the transmission light sources according to the received preciseposition information (S180). For example, the X coordinate of the imagesensor along the X axis or the Y coordinate of the image sensor alongthe Y axis are acquired.

Meanwhile, if the positions along both of the X and Y axes are acquired,position measurement is finished (S190, S200). Otherwise, the flowreturns to the above step S120, and the steps S120 to S180 arerepeatedly performed on an axis along which the position has not beenacquired in order to acquire the position of the image sensor on thecorresponding axis.

Through this procedure, the position, for example, X and Y coordinates,of the image sensor can be acquired.

Next, the structure of the position measuring apparatus according to theexemplary embodiment of the present invention will be described.

FIG. 6 is a schematic view showing the structure of the positionmeasuring apparatus according to the exemplary embodiment of the presentinvention. FIG. 7 is a detailed view showing the structure of theposition measuring apparatus according to the exemplary embodiment ofthe present invention.

As shown in FIG. 6, the position measuring apparatus 100 according tothe exemplary embodiment of the present invention includes a positioninformation receiving unit 110, an inclination measuring unit 120, anactual distance measuring unit 130, a virtual distance measuring unit140, and a position information processing unit 150.

The position information receiving part 110 receives positioninformation transmitted from a plurality of visible-light wirelesscommunication devices 1. The position information receiving unit 110includes an image sensor that captures the position information, i.e.,precise position information, transmitted in the form of optical signalsfrom the visible-light wireless communication devices 1, and outputscorresponding electrical signals.

The inclination measuring unit 120 measures the inclination of theposition measuring apparatus 100. The exemplary embodiment of thepresent invention will be described by taking an example where theposition measuring apparatus 100 is mounted on the mobile terminal 2.The inclination measuring unit 120 measures the inclination of themobile terminal 2 on which the position measuring apparatus 100 ismounted; more specifically, the inclination of the image sensor 111.Since the image sensor 111 may be inclined relative to X and Y axes on atwo-dimensional plane including the X and Y axes, the inclination alongthe X axis and the inclination along the Y axis are measured. To thisend, as shown in FIG. 7, the inclination measuring unit 120 includes anX-axis inclination measuring module 121 and a Y-axis inclinationmeasuring module 122. The inclination measuring unit 120 may include atwo-axis inclination sensor.

The actual light source measuring unit 130 measures the actual lightsource distance between the transmission light sources based on theprecise position information of the visible-light wireless communicationdevices transmitted from the transmission light sources. On thetwo-dimensional plane including the X and Y axes, the actual lightsource distance between the transmission light sources on the X axis andthe actual light source distance between the transmission light sourceson the Y axis are calculated based on the precise position informationprovided from the visible-light wireless communication devices. To thisend, as shown in FIG. 7, the actual light source distance measuring unit130 includes an X-axis actual light source distance measuring module 131and a Y-axis actual light source distance measuring module 132.

The virtual light source distance measuring unit 130 measures thevirtual light source distance between the transmission light sourcesimaged on the image sensor from the image captured by the image sensor111 included in the position information receiving unit 110. That is,the positions (virtual position information) of the transmission lightsources imaged on the image sensor are detected from the captured image,and the virtual distance between the transmission light sources capturedon the image sensor is measured based on the distance between pixels ofthe image sensor. In this case as well, on the two-dimensional planeincluding the X and Y axes, the virtual light source distance betweenthe transmission light sources on the X axis and the virtual lightsource distance between the transmission light sources on the Y axis arecalculated based on the virtual position information acquired from theimage. To this end, as shown in FIG. 7, the virtual light sourcedistance measuring unit 140 includes an X-axis virtual light sourcedistance measuring module 141 and a Y-axis virtual light source distancemeasuring module 142.

The position information processing unit 150 measures the currentposition based on the precise position information, the actual lightsource distance, inclination, and the virtual light source distanceprovided from the visible-light wireless communication devices. Althoughthe current position to be measured herein is the current position ofthe image sensor 111, it ultimately refers to the position of an object(e.g., mobile terminal) on which the position measuring apparatus 100 ismounted.

As shown in FIG. 7, the position information processing unit 150includes a distance measuring module 151, a position calculation module152, and a distance conversion module 153.

The distance measuring module 151 measures the actual distance to theimage sensor corresponding to a measurement position based on theinclination, the actual light source distance between the transmissionlight sources, and the virtual light source distance between thetransmission light sources. Here, the actual distance represents thefirst distance d1 from a certain transmission light source to the imagesensor and the second distance d2 from another transmission light sourceto the image sensor, as shown in FIG. 2, based on the actual positionsof the transmission light sources. To measure the actual distance, thesecond light source distance, which is the virtual light source distancein the parallel state, is calculated based on the virtual light sourcedistance (first virtual light source distance) provided from the virtuallight source distance measuring unit 140 and the inclination providedfrom the inclination measuring unit 120 through the above procedureshown in FIG. 5. Next, the first virtual distance sd1 and the secondvirtual distance sd2 relative to the central point of the image sensorare calculated based on the second light source distance. Then, thefirst distance d1 and the second distance d2, which are the actualdistances, are calculated based on the calculated first and secondvirtual distances sd1 and sd2 and the actual light source distance.

The distance measuring module 151 measures the actual distance along theX axis and the actual distance along the Y axis based on a two-axisplane. To this end, as shown in FIG. 7, the distance measuring module151 includes an X-axis actual distance measuring module 1511 and anactual distance measuring module 1512.

The position calculation module 152 calculates the position of the imagesensor, i.e., the position of a measurement object, based on the actualdistance measured based on the received precise position information oftransmission light sources and the virtual distance on the image sensor.In this case, the actual position on a given axis is calculated byadding or subtracting the actual distance to or from the actual positioncoordinates based on the received precise position information. Byperforming this procedure for each axis, the X coordinate of the actualposition and the Y coordinate of the actual position are calculated. Thethus-calculated X and Y coordinates correspond to the position of themeasurement object. To this end, as shown in FIG. 7, the positioncalculation module 152 may include an X-axis position calculation module1521 and a Y-axis position calculation module 1522.

The distance conversion module 153 converts virtual distance into actualdistance; more specifically, converts measured virtual distance intoactual distance by using a unit virtual distance based on a pixeldistance on the image sensor.

Further, as shown in FIG. 6, the position measuring apparatus 100according to the exemplary embodiment of the present invention mayfurther include a processing method determination unit 160. Theprocessing method determination unit 160 allows position measurement tobe performed in different methods depending on the number of receivedposition information sets. That is, a processing method is determineddepending on the number of position information sets received from thetransmission light sources. For example, if there is one receivedposition information set, position measurement is performed based on thecentral point of the image sensor, the received precise positioninformation, and the positions of the transmission light sources imagedon the image sensor.

On the other hand, if there are two or more position information,position measurement is performed without using the central point of theimage sensor. That is, position measurement is performed based on thereceived precise position information and the positions of thetransmission light sources imaged on the image sensor.

The method of performing position measurement without using the centralpoint of the image sensor is referred to as the “first method”, and themethod of performing position measurement using the central point of theimage sensor is referred to as the “second method”.

If position measurement is performed according to the second method, theprocessing method determination unit 160 provides information on givencoordinates of the central point of the image sensor to the virtuallight source distance measuring unit 130, and calculates the virtuallight source distance based on the central point of the image sensor andthe positions of the transmission light sources imaged on the imagesensor. Afterwards, the actual light source distance between the actualposition according to the precise position information of thetransmission light sources and a measurement position is measured basedon the calculated virtual light source distance. In this case, theprocess for converting virtual distance into actual distance can becarried out. The conversion process may be carried out by using unitvirtual distance, or by using a distance conversion table.

Next, a position measuring method according to another exemplaryembodiment of the present invention will be described based on theabove-described structure.

FIG. 8 is a position measuring method according to another exemplaryembodiment of the present invention.

First of all, the position measuring apparatus 100 determines whetherinclination measurement is possible before it performs positionmeasurement (S300).

If inclination measurement is not possible, an alarm message forinstructing the image sensor to be kept as horizontal as possible can beoutput in order to minimize an error in a measurement position (S310).

The position measuring apparatus 100 captures an image including anoptical signal sent from a transmission light source L of avisible-light wireless communication device 1, and performs theprocessing of the captured image to acquire precise position informationtransmitted from the transmission light source L (S320).

The position measuring apparatus 100 determines if there are two or moreprecise position information sets acquired by this process (S330). Ifso, position measurement is performed according to the first methodbased on the acquired precise position information (S340).

When position measurement is performed according to the first method,the position measuring apparatus 100 calculates the actual light sourcedistance on each of the X and Y axes based on the received preciseposition information of the transmission light sources (S350), and thevirtual light source distance on each of the X and Y axes is calculatedfrom an image captured by the image sensor (S360). Next, when aninclination occurs due to the movement of the mobile terminal on whichthe position measuring apparatus 100 is mounted, the state of the imagesensor 11 changes. Thus, the inclination along each of the axis of theimage sensor 111 and the Y axis is measured (S370 and S380). In thiscase, if inclination measurement is not possible, an alarm message forinstructing the image sensor to be kept as horizontal as possible can beoutput in order to minimize an error in a measurement position (S390).

Afterwards, the actual distance to the image sensor corresponding to themeasurement position is measured, as shown in FIG. 5, based on theactual light source distance, virtual light source distance, andinclination along each of the measured axis and the Y axis (S400).

The position of the mobile terminal is measured based on thethus-acquired actual distances (first distance d1 and second distanced2) to the image sensor along each of the X and Y axes and the preciseposition information of the transmission light sources.

In the exemplary embodiment of the present invention, to achieve moreprecise position measurement, it is determined whether the actualdistance to the image sensor along each of the X and Y axes is aconverted distance (S410). In other words, distance conversion may berequired to compensate an error caused by the use of virtual distancebecause the actual distance is calculated using the virtual distancebased on a pixel distance on the image sensor. If the measured actualdistance has not been converted, the position measuring apparatus 100performs conversion on the measured actual distance (S420). For example,if the virtual distance is a 15-pixel distance, it may be converted intoan actual distance of 1 m by the conversion process. During thisconversion process, a unit virtual distance according to the aboveEquation 3 may be used. Alternatively, the conversion may be performedusing a given virtual/actual distance conversion table. This conversionprocess may be selectively performed.

The position measurement apparatus 100 measures the position of themobile terminal based on the actual distances (first distance d1 andsecond distance d2) to the image sensor along each of the X and Y axesand the precise position information of the transmission light sources(S430).

Meanwhile, if there are less than two precise position information setsreceived in the step S330, the position measuring apparatus 100determines whether the number of the precise position information setsis 1 (S450). If so, the position measuring apparatus 100 decides tomeasure position according to the second method (S460). When performingposition measurement according to the second method, only one preciseposition information set about the transmission light sources isreceived, and therefore position measurement is performed based on givencoordinates of the central point of the image sensor. The coordinates ofthe central point of the image sensor are predetermined. A virtual lightsource distance is measured based on the given coordinates of thecentral point of the image sensor (S460), and inclination measurement isperformed, as described above, based on the measured virtual lightsource distance, followed by the subsequent processes. In this case, thevirtual light source distance is calculated based on a given centralpoint of the image sensor, and the second virtual light source distancecorresponding to the image sensor in the parallel state is calculatedbased on the calculated virtual light source distance and theinclination. Rather than obtaining the first distance d1 and the seconddistance d2 based on the second light source distance as in the firstmethod described above, the actual light source distance can becalculated directly based on the second virtual light source distance,and then the actual position of the mobile terminal can be measured fromthe precise position information of one transmission light source basedon the actual light source distance. In this case also, the conversionof virtual distance into actual distance can be carried out. Theconversion process may be carried out by using unit virtual distance, orby using a pre-created distance conversion table.

After the position measurement, the position measurement may continueoptionally (S470). Otherwise, the position measurement is completed.

According to these exemplary embodiments of the present invention, theposition of a measurement object can be measured more accurately basedon the precise position information of transmission light sourcesreceived from a visible-light wireless communication device, the actuallight source distance based on this information, and the virtual lightsource distance of the transmission light sources imaged on the imagesensor.

The order of the steps of the position measuring method of FIG. 8 ismerely an example, and this order may be changed in some cases.

According to an exemplary embodiment of the present invention, in thecase of position measurement using a visible-light wirelesscommunication technology, position can be measured more accurately byusing information provided from the visible-light wireless communicationdevice, information on the image sensor, and inclination information.

Moreover, the position of a mobile terminal, such as a smartphoneequipped with an image sensor and an inclination sensor, can be measuredwithout the use of additional parts.

The above-described methods and apparatuses are not only realized by theexemplary embodiment of the present invention, but, on the contrary, areintended to be realized by a program for realizing functionscorresponding to the configuration of the exemplary embodiment of thepresent invention or a recording medium for recording the program.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A position measuring method, which measures aposition based on information provided from at least one communicationdevice including a transmission light source, the method comprising:acquiring precise position information indicating a position of thetransmission light source by capturing an image including an opticalsignal transmitted from the transmission light source; calculating anactual light source distance between transmission light sources based onthe precise position information; calculating a virtual light sourcedistance between the transmission light sources imaged on the imagesensor from the captured image; measuring inclination of the imagesensor; and measuring a position based on the actual light sourcedistance, the virtual light source distance, and the inclination,wherein the position measuring comprises: calculating a first virtuallight source distance between the transmission light sources imaged onthe image sensor, and a second virtual light source distancecorresponding to a parallel state of the image sensor based on theinclination; and calculating the position based on the second virtuallight source distance, the actual light source distance, and thereceived precise position information about each transmission lightsource.
 2. The method of claim 1, wherein the position calculatingcomprises: calculating a first virtual distance to one transmissionlight source imaged on the image sensor from a central point of theimage sensor based on the second virtual light source distance;calculating a second virtual distance to another transmission lightsource imaged on the image sensor from the central point of the imagesensor based on the second virtual light source distance; andcalculating the position based on the first virtual distance, the secondvirtual distance, the actual light source distance, and the preciseposition information.
 3. The method of claim 2, wherein, in the positioncalculating, the position is calculated based on the first virtualdistance and the second virtual distance that are proportional to afirst distance and a second distance, the first distance correspondingto a distance from a position of one transmission light source to aposition to be measured based on the precise position information, andthe second distance corresponding to a distance from a position ofanother transmission light source to the position to be measured basedon the precise position information.
 4. The method of claim 3, whereinthe position calculating comprises: calculating the first distance basedon a condition d1=(d1+d2)×sd1/(sd1+sd2) (where d1 represents the firstdistance, d2 represents the second distance, sd1 represents the firstvirtual distance, and sd2 represents the second virtual distance); andcalculating the position according to the position of one transmissionlight source based on the precise position information and the firstdistance.
 5. The method of claim 4, wherein, if the position of onetransmission light source based on the precise position information is acoordinate x1 on an X axis, a coordinate of the position to be measuredcorresponds to a coordinate of x1+ the first distance.
 6. The method ofclaim of claim 1, wherein, if the position is measured on atwo-dimensional plane using X and Y axes, the precise positioninformation comprises coordinates along the X and Y axes, and X-axis andY-axis coordinates of the measurement position are obtained byperforming, for each of the X and Y axes, the acquiring of preciseposition information, the calculating of an actual light sourcedistance, the calculating of a virtual light source distance, themeasuring of an inclination, and the measuring of a position.
 7. Aposition measuring method, which measures a position based oninformation provided from at least one communication device including atransmission light source, the method comprising: acquiring preciseposition information indicating a position of the transmission lightsource by capturing an image including an optical signal transmittedfrom the transmission light source with an image sensor, the preciseposition information including coordinates along X and Y axes on atwo-dimensional plane using the X and Y axes; if the precise positioninformation is received from at least two transmission light sources,calculating an actual light source distance between the transmissionlight sources on each of the X and Y axes based on the precise positioninformation; calculating a virtual light source distance between thetransmission light sources on each of the X and Y axes, imaged on theimage sensor, from the captured image; measuring inclination of theimage sensor along each of the X and Y axes; calculating a parallelvirtual light source distance on each of the X and Y axes, correspondinga parallel state of the image sensor, based on the virtual light sourcedistance and the inclination; and measuring a position of a measurementobject on each of the X and Y axes based on the measured actual lightsource distance, parallel virtual light source distance, theinclination, and the precise position information.
 8. The method ofclaim 1, wherein the position measuring comprises: calculating a firstvirtual light source distance to one transmission light source imaged onthe image sensor from a central point of the image sensor along each ofthe X and Y axes based on the parallel virtual light source distance;calculating a second virtual distance to another transmission lightsource imaged on the image sensor from the central point of the imagesensor along each of the X and Y axes based on the parallel virtuallight source distance; calculating a first distance and a seconddistance for each of the X and Y axes based on the first and secondvirtual distances, the first distance corresponding to a distance to ameasurement position from a position of one transmission light sourcebased on the precise position information, and the second distancecorresponding to a distance to the measurement position from a positionof another transmission light source based on the precise positioninformation; and measuring a position of the object on the X and Y axesbased on the first distance, the second distance, and the preciseposition information regarding the transmission light sources.
 9. Themethod of claim 2, further comprising: converting the first and seconddistances into actual distances, wherein, in the position measuring, theposition is measured using the converted first and second distances. 10.A position measuring apparatus, which measures a position based oninformation provided from at least one communication device including atransmission light source, the apparatus comprising: a positioninformation receiver that acquires precise position informationindicating a position of the transmission light source by capturing animage including an optical signal transmitted from the transmissionlight source with an image sensor, the precise position informationincluding coordinates along X and Y axes on a two-dimensional planeusing the X and Y axes; an actual light source distance measuring unitthat calculates an actual light source distance between transmissionlight sources on each of the X and Y axes based on the precise positioninformation; a virtual light source distance measuring unit thatcalculates a virtual light source distance between the transmissionlight sources on each of the X and Y axes, imaged on the image sensor,from the captured image; an inclination measuring unit that measures aninclination of the image sensor along each of the X and Y axes; and aposition information processing unit that measures a position of ameasurement object on the X and Y axes based on an actual light sourcedistance, a virtual light source distance, and inclination measured foreach of the X and Y axes and the precise position information, whereinthe position information processing unit calculates a parallel virtuallight source distance for each of the X and Y axes, corresponding to aparallel state of the image sensor, based on the virtual light sourcedistance and the inclination, and calculates the position based on theparallel virtual light source distance, the actual light sourcedistance, and the precise position information about each transmissionlight source.
 11. The apparatus of claim 10, wherein the positioninformation processing unit comprises: a distance measuring module thatcalculates the parallel virtual light source distance for each of the Xand Y axes, corresponding to the parallel state of the image sensor,based on the virtual light source distance and the inclination, andcalculates a first distance and a second distance for each of the X andY axes based on the parallel virtual light source distance, the firstdistance corresponding to a distance to a measurement position from aposition of one transmission light source based on the precise positioninformation, and the second distance corresponding to a distance to themeasurement position from a position of another transmission lightsource based on the precise position information; and a positioncalculation module that measures a position of the object on the X and Yaxes based on the first distance, the second distance, and the preciseposition information regarding the transmission light sources.
 12. Theapparatus of claim 11, wherein the position calculation modulecalculates the position based on the fact that the first and secondvirtual distances calculated based on the parallel virtual light sourcedistance are proportional to the first and second distances, the firstvirtual distance corresponding to a distance to the one transmissionlight source imaged on the image sensor from the central point of theimage sensor, and the second distance corresponding to a distance to theanother transmission light source imaged on the image sensor from thecentral point of the image sensor.
 13. The apparatus of claim 11,wherein the position information processing unit further comprises adistance conversion module for converting the first and second distancesinto actual distances.
 14. The apparatus of claim 10, further comprisinga processing method selection unit that selects either a first method ora second method depending on a number of the received precise positioninformation sets, wherein the first method is to measure position basedon the received precise position information, and the second method isto measure position using the received precise position information anda given central point of the image sensor.